President Jacob Zuma, on behalf of the government and the nation, wished Madiba, Mandela's clan name, a speedy recovery and requested the media and the public respect the privacy of the former president and his family.

Mac Maharaj, Zuma's spokesperson, told Al Jazeera Mandela has suffered a lung infection from as far back as he was in prison.

"Because he has grown older ... it [infection] needs more careful attention. This time round he was receiving treatment at home but doctors decided the deterioration was serious [enough] to warrant immediate hospitalisation,” he said.

"So when I describe his condition as serious, I am saying what the doctors have said to me. But they have also added this morning that he is in a stable condition. He is frail and nobody would be prepared to predict how speedily or effectively he would recover."

Keith Khoza, the spokesperson of the governing African National Congress, said Mandela was "in capable hands as he has always been and will pull through".

Media kept away

Al Jazeera's Tania Page, reporting from Johannesburg, said the hospital where Mandela was receiving treatment had not been disclosed as happened with previous admissions because the authorities were trying to keep the media away.

"They don't want a large contingent of media outside the hospital," she said.

"But that in many ways is inevitable because this information does eventually leak out and because there is also such an extraordinary level of attention and care among members of the public as to how he is doing.

"People are aware that he is frail; that he is an elderly man [and] many people are desperate for any news really of his condition."

Mandela, revered at home and abroad for leading the struggle against white minority rule, has been in and out of hospital for lung infection and other health problems.

Last year, he was admitted to a Johannesburg hospital for what officials initially described as tests but what turned out to be an acute respiratory infection.

In March and April, global figures such as US President Barack Obama sent him get-well messages and South Africans included Mandela in their Easter prayers.

Mandela, who became South Africa's first black president in 1994 and served only one term in office, was jailed on Robben Island for 27 years for resisiting white minority rule.